A rocket is sitting on the launch pad. The engines ignite, and the rocket begins to rise straight upward, picking up speed as it goes. At about 1000 m above the ground the engines shut down, but the rocket continues straight upward, losing speed as it goes. It reaches the top of its flight path and then falls back to earth. Ignoring air resistance, decide which one of the following statements is true.
a. Only part of the rocket's motion, from just after the engines shut down until just before it lands, is free-fall.
b. Only the rocket's motion, while the engines are firing, is free-fall.
c. Only part of the rocket's motion, from just after the engines shut down until it reaches the top of its flight path, is free-fall.
d. All of the rocket's motion, from the moment the engines ignite until just before the rocket lands, is free-fall.
e. Only the rocket's motion from the top of its flight path until just before landing is free-fall.